News Release Number: STScI-2008-14

Astronomers Find Suspected Medium-Size Black Hole in Omega Centauri

April 2, 2008: The core of the spectacular globular cluster Omega Centauri glitters with the
combined light of 2 million stars. The entire cluster contains 10 million stars, and
is among the biggest and most massive of some 200 globular clusters orbiting
the Milky Way Galaxy. Omega Centauri lies 17,000 light-years from Earth.
Astronomers at the Max-Planck Institute for Extraterrestrial Physics in Germany and the
University of Texas at Austin have reported on the possible detection of an
intermediate-mass black hole in the core of Omega Centauri.

The result is primarily based on spectroscopic measurements obtained with the
Gemini South observatory in Chile which suggest the stars are moving around the
central core of the cluster at higher than expected velocities. Among the possible
explanations for these speedy stars -- and the one favored by their study -- is that
an intermediate-mass black hole of approximately 40,000 solar masses resides at
the center of Omega Centauri. Its powerful gravitational field speeds up the
motions of stars near the core. Hubble images taken with the Advanced Camera
for Surveys were used in key areas in support of this study: to help pinpoint the
center of the cluster, as well as to measure the amount of starlight at the cluster
center. Using the European Southern Observatory's Very Large Telescope in
Paranal, Chile, team members Eva Noyola and Karl Gebhardt are planning to obtain follow-up
observations to help confirm the existence of an intermediate-mass black hole.
The Hubble images were taken in June 2002.